The increasing interest in thin flexible and bendable devices has led to a strong demand for mechanically robust and electrically reliable transparent electrodes. Indium doped Tin Oxide (ITO) and ...Aluminium doped Zinc Oxide (AZO) are among the most employed transparent conductive oxides (TCO) and their reliability on flexible substrates have thus received a great attention. However, a high flexibility is usually achieved at very low thickness, which, unfortunately, compromises the electrical conductivity.
Here we report the effects of mechanical bending cycles on the electrical and optical properties of ultra thin AZO/Ag/AZO multilayers (45nm/10nm/45nm) and, for comparison, of AZO and ITO single layers whose thickness was, in both cases, 100nm and 700nm, deposited at room-temperature on flexible polyethylene naphthalate (PEN) plastic substrates. The electrical stability of the films after several cycles of bending were evaluated by monitoring the relative variation of the electrical resistance with respect to the as prepared sample; the structural damage induced by bending was detected by Scanning Electron Microscopy (SEM). We observed an excellent electrical stability and high flexibility in the AZO/Ag/AZO sample even after 100 cycles, whereas for the single AZO and ITO films the resistivity rapidly increases. The experimental results and numerical simulations provide clear evidences of the key role played by the ductile Ag interlayer that provides improved robustness under mechanical strain.
•Evidence of good electrical quality of AZO/Ag/AZO ultra thin films without thermal annealing.•Evidence of much better flexibility with respect to films of single AZO and ITO with equal or higher thickness.•Evidence of much lower structural damage compared to films of single AZO and ITO with equal thickness upon bending cycles.•Numerical simulation of strain intensity and distribution within the films during mechanical bendings.•Evidence of the possible use of AZO/Ag/AZO ultra thin films as Transparent Conductive Material for flexible thin devices.
In this paper, novel optimization methodologies of sub-relativistic guided interaction structures for dielectric laser particle acceleration (DLA) are presented. In particular, we focus on ...co-propagating geometries based on slot waveguides in continuous wave (CW) operation, where the particle flow and the direction of propagation of the accelerating field are co-linear. Since the velocity of sub-relativistic particles varies along the acceleration path, proper tapering of the waveguide geometry is required to achieve an extended acceleration region, and, thus a large energy gain. The design of an optimal taper ensuring particle-wave synchronicity and maximum energy gain is pursued through a physics-based approach, and these results are compared, for validation, with the outcomes of a downhill simplex method searching algorithm. Additionally, the application of a simplified 2D model of the accelerating slot waveguide is investigated and profitably used to get qualitative results useful for fast structure optimization. Indeed, this approach can hold significant potential for the development of novel accelerating structures, as it enables a thorough and fast exploration of the design space.
Environment friendly, thin and flexible devices require the synthesis of Indium-free new transparent conducting materials (TCM) with improved structural, thermal, electrical and optical properties. ...To overcome the critical issues raised by thinning the TCM, we propose a multilayer structure in which nanogranular Ag film obtained by supersonic cluster beam deposition is sandwiched in between Alluminum doped Zinc Oxide (AZO) thin layers. The introduction of the nanogranular Ag film, when compared to the standard sputtered one, yields higher optical transmittance in the technologically relevant VIS-NIR region and superior mechanical reliability while preserving low electrical resistance. The present results open new perspectives to exploit the nanogranular nature of conductive films, synthesized via Supersonic Cluster Beam Deposition, to engineer transparent conducting materials.
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•Enhancement of the optical transmittance in the visible and IR range.•Low electrical resistivity of the nanogranular Ag film.•High flexibility and electrical reliability during bending.•Validation of experimental results by numerical simulation.•Implementation of nanogranular ultra-thin films as flexible transparent electrode.
Abstract
We hereby report a study on confinement and electron loss dynamics in the magnetic trap of an electron cyclotron resonance ion source using a special multi-diagnostic setup that has allowed ...the simultaneous collection of plasma radio-self-emission and x-ray images in the range 500 eV–20 keV. Argon plasmas were generated in single- and two-close-frequency heating (SFH and TCFH) modes. Evidence of turbulent regimes has been found: for stable and unstable configurations quantitative characterizations of the plasma radio self-emission have been carried out, then compared with local measurements of plasma energy content evaluated by x-ray imaging. This imaging method is the only one able to clearly separate x-ray radiation coming from the plasma from that coming from the plasma chamber walls. X-ray imaging has also been supported and benchmarked by volumetric spectroscopy performed via silicon drift and high-purity germanium detectors. The obtained results in terms of x-ray intensity signal coming from the plasma core and from the plasma chamber walls permit the estimation of the average ratio: plasma vs. walls (i.e. plasma losses) as a function of input RF power and pumping wave frequency, showing an evident increase (above the experimental errors) of the intensity in the 2–20 keV energy range due to the plasma losses in the case of unstable plasma. This ratio was well correlated with the strength of the instabilities, in SFH operation mode; in TCFH mode, under specific power balance conditions and frequency combinations, it was possible to damp the instabilities, and thus the plasma losses were observed to decrease and a general reconfiguration of the spatial plasma structure occurred (the x-ray emission was more concentrated in the center of the plasma chamber). Finally, a simplified model was used to simulate electron heating under different pumping frequencies, prompting discussion of the impact of velocity anisotropy vs the onset of the instability, and the mechanism of particle diffusion in the velocity space in stable and unstable regimes.
Abstract We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for ...accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The 134 Cs, 176 Lu, and 48 Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the γ activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall γ -detection system’s efficiency using GEANT4, including the poisoning γ -signal from the walls of the trap, relevant for the γ -tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.
Experiments have recently demonstrated that kinetic instabilities occurring in magnetoplasma are huge limiting factors to the flux of highly charged ion beams extracted from ECR ion sources. ...Recently, it has been shown that the two-frequency-heating (TFH) mode has the proven potential to mitigate these instabilities. Since the fundamental physical mechanism of TFH is still unclear, a deeper experimental investigation is necessary. At ATOMKI-Debrecen, the effect on the kinetic instabilities of an argon plasma in a 'two-close-frequency heating' scheme has been explored for the first time by using a frequency gap smaller than 1 GHz (i.e. operating in the so-called two-closed-frequency heating mode). A special multi-diagnostics setup has been designed and implemented. In this paper, we will show the data collected by a two-pin, plasma-chamber immersed antenna connected to an RF detector diode and/or to a spectrum analyzer for the detection of plasma radio-self-emission when varying the pumping frequency in single versus double frequency heating mode. Data have been collected simultaneously to the beam extraction and for different frequency gaps and relative power balances. The turbulent regime of the plasma has been tentatively described in a quantitative way, according to the properties of the plasma self-emitted RF spectrum. The measurements show that plasma self-emitted radiation emerges from the internal ECR region everytime (i.e. below the lower pumping frequency) but the almost total instability damping can be effective for some specific combinations of frequency-gap and power balance, thus eventually improving the plasma confinement.
Abstract
In this paper we present the numerical design and simulation of RF antennas to be employed in Ion Cyclotron Resonance Heating (ICRH) systems working in ECRIS environment. A 3D full-wave ...numerical model, based on the coupling between COMSOL FEM solution of Maxwell equations and the MATLAB-computed non-homogeneous plasma dielectric tensor, has been employed in order to study the performances of several ICRH antennas. Results in terms of S-parameters, on-axis electric field and RF absorbed power inside the plasma chamber have been obtained and compared between the chosen antenna geometries. The presented study will permit to better understand the fundamental aspects of ion dynamics in ECRISs as well as allowing the design of a proper matching network between the RF amplifier and the antenna, necessary to cope with the plasma properties’ fast variations. Further ion kinetic simulations are ongoing.
